www.delorie.com/gnu/docs/calc/calc_91.html

search

	Buy the book!

GNU Emacs Calc 2.02 Manual

3.7.57 Rewrites Tutorial Exercise 6

Just put the rule `0^0 := 1' into EvalRules. For example, before making this definition we have:

2: [-2, -1, 0, 1, 2] 1: [1, 1, 0^0, 1, 1] 1: 0 . . v x 5 RET 3 - 0 V M ^

But then:

2: [-2, -1, 0, 1, 2] 1: [1, 1, 1, 1, 1] 1: 0 . . U ' 0^0:=1 RET s t EvalRules RET V M ^

Perhaps more surprisingly, this rule still works with infinite mode turned on. Calc tries EvalRules before any built-in rules for a function. This allows you to override the default behavior of any Calc feature: Even though Calc now wants to evaluate 0^0 to nan, your rule gets there first and evaluates it to 1 instead.

Just for kicks, try adding the rule 2+3 := 6 to EvalRules. What happens? (Be sure to remove this rule afterward, or you might get a nasty surprise when you use Calc to balance your checkbook!)